nice, in others words i would rewrite it to:
SELECT * FROM t WHERE (data_compensacao_origem || "")<"2012-11-31 24:00:00"

does i will have problems with index optimizations?

could check if leap second will work in mariadb? i didn´t tryed and nobody talked it as an error, maybe never will talk since nobody is using my system at 23:59:60 they normally use between 08:00:00 and 20:00:00, at test 23:59:60 returned a warning (and no result) and it´s a 'legal' datetime value at least to UTC timezone

http://dev.mysql.com/doc/refman//5.5/en/time-zone-leap-seconds.html
"Leap second values are returned with a time part that ends with :59:59. This means that a function such as NOW() can return the same value for two or three consecutive seconds during the leap second. It remains true that literal temporal values having a time part that ends with :59:60 or :59:61 are considered invalid."

nice, but they are for timestamp fields, what about datetime fields? i´m asking because i read some parts of manual and didn´t found the information (i agree with you that mysql isn´t like manual but for a user changing from mysql to maria maybe this could be a problem to port code, for me no problem i can rewrite the query but for someone that have many queries this can be a problem)

in others words...
to allow a easy user port from mysql to mariadb, could we add a new sql_mode option? (feature request)
maybe COMPARE_DATETIME_AS_STRING to make things easier?

i´m considering this as a feature request instead of a bug

please close this bug, i reported a feature request since i understood that mysql isn´t doing a datetime comparision, it´s doing string comparision... \o/ mariadb rocks =)
new feature request id is MDEV-391